Centec Mk3 Vertical Head Rebuild

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Centec Mk3 Vertical Head Rebuild

This topic has 10 replies, 7 voices, and was last updated 8 December 2024 at 16:48 by mark smith 20.

Viewing 11 posts - 1 through 11 (of 11 total)

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7 December 2024 at 16:14 #769269
Graham Horne 2
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@grahamhorne2
I have a Centec 2B horizontal mill with a Mk3 vertical head. I say a Mk 3 as I have watched YouTube videos of the disassembly of the head and earlier heads use a slotted quill housing lock which causes the head itself to tighten the grip on the quill. Mine has a wedge ended shaft with the quill lock using the shaft the wedge that pulls against quill as the lock. I am sure other more experienced folks will highlight the correct technical terminology.

The spindle bearings in the quill are Timken 07100S tapered roller bearings. Getting the tapered bearing cone out of the quill was a pain but a YouTube video by “Beachcomber Bob” helped a lot. Below the bottom bearing is an oil seal. Not sure if it is original but it is not the leather seal other owners found but rather a Weston 2001-3750-R4 lip seal but I can’t seem to source the part. I think it’s called a lip seal. The seal is an imperial 2” outer diameter and 1 3/8” internal diameter. Do I just replace it with the same size no matter the part number?

The drive shaft that runs horizontally connects a belt pulley on the rear and an angular gear drive at the front driving the vertical spindle. This horizontal shaft has Timken 03062 tapered roller bearings once again with the cone pressed into the horizontal body. I can’t see a way to press the cones out as they are pressed into the housing against an internal stop.

Does anybody know of any secrets to get the cones out of the housing body? It looks like my only option is to use a die grinder to weaken the cone at the grease entry slot on the top and then use a chisel to break the cones out. The bearings are in reasonable condition but as I am going to great lengths to rebuild and refinish the head and I want the replace the bearings now while it is being refinished.

My expectation is that with new bearings and the correct grease it can be run a little faster with the VFD than the original speed Centec horizontal mill speed of 1,400 RPM. I note the the shaft pulley size difference allow for around 12% speed increase onto the horizontal head shaft which would mean about 1,570 RPM at the spindle. There was also another Centec model running a 2pole motor and was advertised at a top speed of 2,800 RPM. So I am hoping with careful build and good grease I can get the spindle to around 2,500 RPM without too much heat generated but we will see. For now I just have to get those bear cones out of the head housing.
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7 December 2024 at 17:40 #769282
DC31k
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@dc31k
On 7 December 2024 at 16:14 Graham Horne 2 Said:

Does anybody know of any secrets to get the cones out of the housing body?

An old trick to remove bearing races is to run a bead of weld around the inside. As it cools, it will shrink the race and it will nearly fall out.

Remember that as originally designed, the machines were for industrial use, 8h a day, 5 days a week. Of those 40 hours per week for how many of them will the machine run at top speed now it is under your stewardship?
7 December 2024 at 18:20 #769286
noel shelley
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@noelshelley55608
DC3 has the answer IF you have access to an arc welder. use a 2.5 mm rod and dont leave to much of a bead. It all depends on just how the bearing is fitted It may have a cutout that will let you use a punch, if the cone over hangs the seat then a small bearing puller will work. Good luck. Noel

The seal, try 137 x 200 x the width eg 37 for 3/8″. Have you got prices for the bearings – good ones – you may think twice. N
7 December 2024 at 18:56 #769304
old mart
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@oldmart
I used a seal on the Tom Senior light vertical R8 conversion and had no end of bother with spindle overheating which I mistook for too much preload. The seal was exactly matched to the ground end of the spindle, and I chose a double lipped seal. A minimal exterior lip and a common inner lip with a garter spring. When I eventually realised that the upper taper roller bearing was not getting hot the seal became the prime suspect. I had reduced the grease in the spindle to about 20% in case of churning which made no difference. Only completely cutting off the inner seal solved the heating and with common lithium high melting point grease used with older car and motorcycle wheel bearings, there was no tendency for any to run out of the base of the spindle, and the tiny outer lip serves to prevent swarf getting into the bearing. Any make except Castrol which tends to separate and allow the oil content to migrate where its not wanted.

There are several online seal and bearing suppliers in the UK who don’t mind small orders, I bought an SKF metric taper roller for the bottom and an original inch size Timken for the top.
8 December 2024 at 11:23 #769351
Dave Halford
Participant
@davehalford22513
All the Centec bearings seem to be intended to tap in with a drift in like the gearbox although there are no internal shoulders or circlips in the column. Can you get behind and tap the bearing out?

The high speed Centec has the same internals
8 December 2024 at 13:05 #769395
Graham Horne 2
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@grahamhorne2
IF you have access to an arc welder. use a 2.5 mm rod and dont leave to much of a bead.

I had a close look at the possibility of running a bead of weld on the bearing cone to shrink it slightly. I only have a MIG/TIG welder. I assume it would still work with MIG. The difficulty is the bearing cone is very deep and the housing is only 1 5/8” diameter. I could splatter grease over things to stop MIG splatter getting on the bearing housing but to be honest I am nervous to do this weld.</p>

Can you get behind and tap the bearing out?

There is a single small machined step behind the cone on the top side where grease can be forced into the bearing down a hole from the external nipple but the housing stop diameter is much less than the internal diameter of the cone so it can’t be pushed from inside. The small step is also only on the topside so I can get a bearing puller in there. I don’t think the manufacturer ever planed for these to be replaced.

I have one other issue as well. The bearing at the top of the vertical housing (not in the quill) that runs the drive through which the spline on the spindle travels is also being problematic and I am yet to get it apart. The bearing housing removes easily from the vertical housing. On one side there is an angle gear that meshes with the gear from the horizontal shaft. On the top there is a large 4-slot slotted round nut that seems to hold bronze gear and female spline shaft drive into the bearing assembly. I also assume the slotted nut screws onto the spline shaft drive but I can’t see to confirm. You would think it’s a slotted nut must be unscrewed so you could use an adjustable pin spanner to remove.

So I just wanted to confirm if the slotted nut truly does unscrew as it is still unmovable. I have tried heat but it won’t seem to budge. Any ideas? Does this unscrew? The single adjustable spanner is at its limits I fear. Maybe I need to make a 4 pin spanner, heat and a hammer.
8 December 2024 at 13:18 #769401
Graham Horne 2
Participant
@grahamhorne2
Remember that as originally designed, the machines were for industrial use, 8h a day, 5 days a week. Of those 40 hours per week for how many of them will the machine run at top speed now it is under your stewardship?

The speed is just about small mills at higher speeds. The stress is the speed and not the cutter load.
8 December 2024 at 14:33 #769412
not done it yet
Participant
@notdoneityet
My suggestion is to PM Gary Wooding. He is the resident expert on Centecs but seems not to have posted recently, even though he has been on the forum quite recently.

Question: could the bearing seat be milled away in two opposite spots, to be able to drift out the bearing cone?
8 December 2024 at 15:59 #769447
Dave Halford
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@davehalford22513
I would wash the grease out of the rollers and check for glitter, if there isn’t any, then why change the bearing?
8 December 2024 at 16:21 #769449
Graham Horne 2
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@grahamhorne2
I would wash the grease out of the rollers and check for glitter, if there isn’t any, then why change the bearing?

To be honest that’s looking like a good option. It’s just the amount to refurbishing that goes into something like this properly, then the price of bearings is almost irrelevant but this looking a bridge too far. I don’t have experience and judgement of an engineer. So I don’t know what is best so I put it out there to garner the experience of those who know more. I’m a woodworker and these tools are to rebuild my woodworking machines and template or protype new tools I make but I sure enjoy learning about precision engineering.
8 December 2024 at 16:48 #769450
mark smith 20
Participant
@marksmith20
Different mill ,different bearings but i replaced some bearings in my alexander , it hadnt been used for years but i managed to find some old unused Hofmann bearings on ebay.The bearing were rusted and pitted due to lack of use for years and lack of oil/grease.So it is worth checking the bearings if your taking the head apart.
The grease i used was called Kluber isoflex NBU 15 ,expensive for a small tube but hardly used much.
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